The primary objective of this study was to investigate and define the possible mechanism(s) by which the pathophysiological states of sodium retention and fluid volume expansion occur after a single ethanol administration. As delineated in the specific aims, we recorded alterations in blood gases, blood bicarbonate, pH, and fluid balance after a single ethanol dose (3 gm/kg) to the dog. The results of this study allowed us to identify a correlation between positive water balance and decreases in blood bicarbonate concentration during the descending plasma ethanol curve, i.e., 10-21 hr after ethanol treatment. In a second study the relationship between fluid volume expansion and altered bicarbonate reabsorption was investigated. The results demonstrated that the renal diuretic and natriuretic sensitivity to a hypertonic sodium-bicarbonate infusion was significantly blunted by the ethanol administration. In other words, it appeared that the renal capacity for bicarbonate reabsorption was significantly enhanced after the ethanol administration 18 hr after a single dose (3 gm/kg). An alternative conclusion, however, was that the response was due to the sodium ion, rather than bicarbonate, or that the response was due to a differential sensitivity of the animals to a hypertonic infusion. Both alternatives were investigated in the same animal model. The results of both studies clearly demonstrated that neither alternative hypothesis could explain the results. The results to date demonstrate that after a single ethanol administration there was a correlation between positive water balance and decrease in blood bicarbonate concentration. The results also demonstrate that renal bicarbonate reabsorptive capacity was enhanced after the ethanol dose and that apparently increments in sodium and water reabsorption were dependent on the bicarbonate response.